1. Field
Embodiments relate to a secondary battery.
2. Description of the Related Art
Currently, compact and light electric/electronic devices such as cellular phones, laptop computers, and camcorders are being actively developed and produced. These portable electric/electronic devices include a battery pack so as to operate at places where no power source is provided. The battery pack may include a secondary battery that is rechargeable and dischargeable, and may output a certain level of voltage to drive a portable electric/electronic device for a certain period of time. A battery pack may also be used to power a motive power source, such as in an electric or hybrid vehicle.
Secondary batteries include, for example, nickel (Ni)-cadmium (Cd) batteries, Ni-hydrogen (H) batteries, and lithium (Li) batteries. Li secondary batteries may have a operation voltage of about 3.6V, which is about three times higher than that of Ni—Cd batteries or Ni—H batteries, and may have a high energy density for unit weight. Thus, Li secondary batteries are increasing in popularity.
Li secondary batteries may use a Li-based oxide as a positive electrode active material and a carbon material as a negative electrode active material. In general, according to the type of electrolyte, Li secondary batteries may be classified as liquid electrolyte batteries and polymer electrolyte batteries. Li secondary batteries using a liquid electrolyte may be referred to as Li ion batteries, and Li secondary batteries using a polymer electrolyte may be referred to as Li polymer batteries. Li secondary batteries are manufactured in various shapes such as a cylinder shape, a rectangular shape, and a pouch shape.
A Li ion secondary battery may include an electrode assembly in which a positive electrode plate (on which a positive electrode active material is coated), a negative electrode plate (on which a negative electrode active material is coated), and a separator (disposed between the positive and negative electrode plates so as to prevent a short and to allow movement of Li ions) are wound or stacked. The Li ion secondary battery may also include a case for accommodating the electrode assembly, and an electrolyte injected into the case so as to allow movement of Li ions.
In a Li ion secondary battery, the electrode assembly may be formed by winding or stacking the positive electrode plate (on which the positive electrode active material is coated and to which a positive electrode tab may be connected), the negative electrode plate (on which the negative electrode active material is coated and to which a negative electrode tab is connected), and the separator. The positive electrode active material may contain a complex Li oxide as a main component, e.g., LiCoO2, which may be formed by mixing carbonic acid, Li, and cobalt (Co) oxide in a ratio of 1.2:1 and baking the mixture at a temperature of about 400° C. to about 1000° C. The Li secondary battery may be completed by accommodating the electrode assembly into the case, injecting the electrolyte into the case, and then sealing the case.
When the Li secondary battery is repeatedly recharged, the electrode assembly may repeatedly expand and contract. The expansion and contraction of the electrode assembly may cause a swelling phenomenon such that the case may expand.